Hydraulic system embodying means for depressurizing cylinders without shock



Ian. 15, 1963 w. VAN DOORN ETAL 3,0 HYDRAULIC SYSTEM EMBODYING MEANS FORDEPRESSURIZING CYLINDERS WITHOUT SHOCK Filed Aug. 9, 1960 3 Sheets-Sheet1 INVENTORS.

Dona/0 1/1/- Mi BY William C. Peas-e 111 3,073,287 OR DEPRESSURIZING 3Sheets-Sheet 3 .Do U VanDoorn. BY Wifi/ZM. C. Pease 1F D. W. VAN DOORNET AL HYDRAULIC SYSTEM EMBODYING MEANS F CYLINDERS WITHOUT SHOCK T W HF-22 T m w. M; mum 1 H m2 QT V J J x v M H 9m 3 w: n

s 3 mm V SE v N F m i S 2 ma R 7 QMQ\ v% +8 Jan. 15, 1963 Filed Aug. .9,1960 United states Patent() HYDRAULIC SYSTEM EMBODYING li lEANS FGRDEPRESSURIZHNG CYLINDERS WETHUUT SHQCK Donald W. Van Doom and William G.Pease HI, (Iolumbus, Ga assignors to Lurnmus Cotton Gin Company,

a corporation of Georgia Filed Aug, 9, 1960, Ser. No. 48,526 9 Claims.(Cl. 121-38) Our invention relates to hydraulic systems and has for itsprincipal object the provision of means associated with such systemswhereby upon depressurizing a hydraulic cylinder or other pressuredevice, depressurization is accomplished without hydrauli shock. I

In the art to which this invention relates it is known that tremendoushydraulic shock is obtained in the conduits, valves and other parts ofhydraulic systems when high pressure cylinders or the like aredepressurized. That is, in systems heretofore existing, such forinstance as in hydraulic systems for baling cotton and the like, whenthe main valve controlling the admission of fluid under pressure to thecylinder was opened, shocks of extremely high order were imposed on theconduits and other parts of the equipment. In presses which operate ataround 2,000 pounds per square inch, this sudden release of high.volume, high pressure oil when the cylinder is depressurized has causedserious damage to the piping and the like. It has been possible,heretofore, to solve this problem in part. However, the apparatusnecessarily employed to accomplish this improvement has been complicatedand expensive, almost to the degree that its use has been prohibitive oncertain types of equipment.

In view of the foregoing a prime object of our invention is to provideapparatus which is economical, simple and trouble free in operation andwhich may be associated with hydraulic systems embodying high pressurecylinders, rams or the like and which is effective to permit the ram tobe depressurized without any appreciable hydraulic shock to the system.

Another object of our invention is to provide apparatus of the characterdesignated which is applicable both to single acting and double actingcylinders or rams.

Another object is to provide depressurization means for high pressurerams or the like in which we provide, in fluid lay-passing relation tothe main flow valve, a smaller valve together with means to open thesmaller valve prior to opening the main valve, thereby bleeding oil arelatively small quantity of the total quantity of fluid, relieving thepressure and thereby permitting the main valve subsequently to openwithout producing the aforementioned hydraulic shock or hammer in thelines.

Another object of our invention is to provide depressurization means forboth double and single acting hydraulic cylinders which is ellective forthe purposes indicated without materially increasing the length of timerequired to bring the cylinder up to pressure and without materiallyincreasing the length of time required to depressurize the cylinder.

A further object is to provide a pilot or control valve associated withthe main valve in such manner that the actuation of the pilot valve todepressurize the cylinder also automatically brings into operation thesubsequent opening of the main valve, whereby the main valve either isopened or permitted to open simply by the operation of the pilot valve.

Briefly, we show our invention as being associated alternately with asingle acting and a double acting ram. In the former case we prefer touse a spring loaded, differential piston main valve together with checkvalves and a spring loaded check valve associated therewith and a pilotvalve eficctive to control the operation of the main valve. In essence,we so arrange the spring loaded check valve and the small hydraulicpilot lines relativeto the main valve that on the larger end of thedifierential piston thereof, in initial operation of the system, thereis developed enough pressure to overcome a spring provided in the mainvalve, thereby to close oil the return port from the cylinder to thereservoir. When the pressure in the main line, which is applied to thesmall end of the valve and also to the large piston end, drops below thepressure of the spring, then the spring in the diflerential piston valvecomes into play and opens the valve.

In the case of the double acting cylinder we preferably employ a main,spool type four-way valve which is hydraulically operated from the pilotvalve. That is, we provide a main valve which has a spring return toneutral position and move the spool thereof to proper'operating positionby hydraulic connections from the pilot valve.

As the description proceeds, it will be apparent that our inventionembodies the concept of maintaining a hydraulic unbalance which holdsthe main valve closed during the period of time that the cylinder isbeing depressurized. The high pressure fluid is bled off through a smallpilot valve or the like until the system pressure lowers to a point thatis safe to allow the main valve to open without shock to the system. Atthis pressure the hydraulic unbalance changes allowing the main valve toopen, eliminating hydraulic shock or hammer. Further, our invention isparticularly adapted for use in connection with fiber presses such ascotton baling apparatus. 'Therefore, we show in this applicationsuitable electrical controls as a part of our system and which make ourinvention en-.

tirely suitable for the operation and control of baling presses.

Apparatus illustrating features of our invention is shown in theaccompanying drawings, forming a part of this application, in which:

FIG. 1 is a wholly diagrammatic view with certain parts in section andshowing a system embodying our invention which is adapted for operationof single acting rams;

FIG. 2 is a detail sectional view taken along line 2-2 of FIG. 1 andshowing a detail of the main valve;

FIG. 3 is a wholly diagrammatic wiring diagram especially constructedfor operating the single acting ram of FIG. 1;

FIG. 4 is a wholly diagrammatic view showing our invention inassociation with the hydraulic system for op erating a double actingram; and,

FIG. 5 is a sectional view through the main valve of FIG. 4.

Referring now to the drawings and particularly to FIGS. 1 and 2, we showin diagrammatic manner a ram of the single acting type indicated at 1%.The plunger of the ram is indicated at 11. For the purpose ofillustration, ram 11 may be the ram for the packing element of anup-packiug cotton baling press. The cylinder is PIG? vided with an inlet12 adjacent its bottom for the admission of fluid under pressure fromthe source presently to be described.

At 13 we illustrate an electric motor which is shown diagrammatically asdriving a hydraulic pump 14. A reservoir for the fluid used is shown at15. The pump may be provided with an automatic relief valve shown at 16and which is in the main pressure line 17. A return line 18 leads fromthe pressure relief valve 16 back to the reservoir 15, in the usualmanner.

In the pressure line 17 we insert a spring biased check valve 20. Thepressure line then leads to the connection 12. A branch line 19 of thehigh pressure line leads to an opening 21 in the housing of the mainfio'w control valve 22 of our system which will now be described.

The main control valve 22 embodies a hollow movable piston or plunger 23which cooperates at 24 with the valve body to form a sealing seat, thusto close off passage 21 of the valve housing from a passage 26 therein.The passage 26 is connected by line 27 to return fluid to the reservoir15.

The plunger 23 is biased downwardly by means of a compression spring 28which rests with one end on the seat 29 of the hollow plunger 23 and atits other end against a shoulder 31. The shoulder 31 is convenientlymounted on the end of a pin 32. The upper end of the pin is welded to amember 33 that forms a T with pin 32 which is mounted in suitable mannerin the valve body. An O-ring seal 34 may be provided.

It will be noted that the end 23 of the movable piston 23 adjacent theopening 21 is smaller in area than the end 23, which latter endhereinafter will be referred to as the pilot end of the piston. t willfurther be seen that by properly proportioning the etlective areas ofthe ends 23 and 23 and the pressure exerted by spring 28, we are enabledto obtain a valve which can be operated as hereinafter will beexplained.

Adjacent the pilot end 23 of the piston we provide a fluid dischargeopening 36. At 37 we show an opening in communication with opening 36and which is connected by a small branch line 38 to a small line 39. Theline 39 is connected through a small check valve 41 to a branch line 42leading to the main branch line 19. The line 38 is connected by a line43 and through a small check valve 44 to a small line 46. The line 46 isconnected at 47 to the main line 17 at a point between the pump 14 andthe spring loaded check valve 20.

At 48 we show a small four-way spool type valve which may be undercontrol of a solenoid 49 and a return spring. sufiice it to say that thevalve 48 of the type that when the solenoid operator 49 therefor isdeenergized, oil is free to flow from the pilot end 23 of a valve 22through a line 51, port B, out port T, to a line 52 and thence to thetank through a line 53. Also, and as a matter of giving more volume offlow as will later appear, the valve 48 may be double ported so thatfluid also flows, when the solenoid 49 is deenergized, from the port 36through a line 56 to port P, thence to port A of valve 48, and through aline 57 to the line 53 and on to the tank. When the solenoid isenergized the spool of valve 48 is moved so as to connect port A with Tand B with P. The net effect of energizing the solenoid 49 therefore isto block the flow of oil from the pilot end of the main valve 22 to thereservoir 15.

Referring now to FIG. 3 of the drawings, we will now describe a suitableform of electrical circuit which adapts our invention to associationwith a press for baling cotton and like fibers. As will be understood,in the baling of cotton or similar fibers it is necessary to exertpressures on the order of 2,000 pounds per square inch. Once the bale iscompressed ties or the like are placed around it to restrain it againstexpansion, the ram is then lowered (in the case of the up packing orsingle action ram), the bale is removed, the ram is raised again todress the block, that is, to place the bagging about the block carriedby the ram, and the ram is again lowered. With modern-day, fullyautomated, power driven, two box presses, it is also necessary to beassured that the ram is out of the press box while the box moves fromone position to the other. Therefore, it is for the purpose ofcorrelating these several motions that the electrical circuit now to bedescribed is designed to cooperate with our improved hydraulic circuit.

Referring now to FIG. 3 power for the several devices may be suppliedthrough lines L and L as shown. At 61 we show a normally closed pushbutton switch 61 in the line L A switch 62 is a stop switch and may be agang type switch having separate tiers 63, (normally closed) 64(normally open) and 66 (normally open). The up switch is indicated at 67and may have an upper tier 68, and a lower tier 69, both normally open.

It will be seen from FIG. 3 that the line L may be connected, when allof the switches 61, 62 and 67 are closed, to the coil 70 of a relay.Relay 7% has a contact'arm 71 having thereon a pair of movable contacts71 and 71 which cooperate with stationary contacts 72 and 73. It will beapparent that the contact 72 cooperates with the movable contact 71 onarm 71 to form a holding circuit for coil 70 whenever the tier 64 ofswitch 62 is closed; and that contact 73 cooperates with its contact 71on arm 71 to form a holding circuit for coil 70 whenever the tier 68 ofswitch 67 closes. Furthermore, it will be seen that we provide a relayhaving a coil 74 having a switch arm 76 carrying a contact point tocooperate with a stationary contact 77. When the switch 67 is closed itenergizes and locks in the control relay coil 70, also starting themotor 13 for the hydraulic pump 14. Closing the up switch 67 alsoenergizes and locks in control relay coil 74, energizing the solenoid 49controlling the pilot valve 48. Pushing and then releasing the stopbutton of switch 62 deenergizes control relay coil 70, stopping thepump. Pushing the down switch 61 deenergizes both the coil- 74 and thesolenoid 49. Likewise, pushing the stop switch 62 energizes and locks inthe relay coil 74 and the sole noid 49 controlling the valve 48. It willbe apparent that it also momentarily energizes the pump motor so long asthe stop switch 62 is held depressed. The importance of this will laterappear.

Considering now the operation of the mechanism so far described andassuming the piston 11 of the ram to be in lowered position and that itis desired to raise the ram to compress a bale of cotton in a pressabove the ram, the following action takes place:

The up switch 67 is momentarily closed, having the effect of energizingthe electric motor 13 for the pump 14 and energizing the solenoid 49 ofvalve 48. When the solenoid 49 is energized the spool of valve 48 movesto align the port B with P and the port A with T. The eifect of this ismerely to block off any exit of oil from the pilot end 23 of the valve22, shutting off any ilow of fluid from the pilot end port 36 back tothe reservoir 15. As has been stated, in the deenergized position of thesolenoid 49 oil would be allowed to flow from the pilot end 23* of valve22 back to the reservoir 15. It might here be mentioned that the onlyreason for having a double ported valve 48 is that we are able to use avery small inexpensive valve and still provide for the trequired How ofoil. Having now momentarily closed the switch 67, it will be rememberedthat th pump 14 is being driven and that the valve 48 is connected ashas just been described. Oil flows from the pump discharge up throughthe relief valve 16 where it encounters the spring loaded check valve20. At the commencement of this operation the piston or movable body 23of valve 22 will be in its lowered position with the seat 24 open,permitting any fluid in line 1'] to pass through the port 21, outthrough the port 26 and back to reservoir 15. However, since we haveprovided the spring check valve 20, fluid under low pressure of theamount that the spring of valve 20 will produce (for example, 75 poundsper square inch), flows through the line 46, past checked valve 44,through line 33 into port 37 and thence into the pilot end of valve 22.in.

view of the fact that the area of the end 23 of the movable plunger 23is very large (for example, 8.5 square inches), the low pressuredeveloped by the spring loaded check 2! is suflicient to develop enoughforce to overcome the downward push (for example, 400 pounds), on theplunger exerted by spring 23. This will cause the plunger 23 to moveupwardly and close off the flow of the oil from port 21 to port 26 byseating at 24. As soon as the plunger of valve 22 closes pressure buildsup in the main line 1'7 leading to the ram. However, due to 75 poundsper square inch pressure drop through valve 243 and the differential inareas on the top and bottom of piston 23 (for example, top area 7.5square inches, bottom area 8.5 square inches) there will be insufficientpressure on the upper end 23 to Open the valve 22. Therefore, the ram 11rises and presses the bale to whatever density the press is set at,usually being on the order of 2,000 pounds per square inch. At thispoint the stop button is pressed which stops the pump motor.

Let it be assumed, now, that the ram is pressing against the bale at2,000 pounds per square inch. It will be apparent that if the largeplunger 23 by some means were suddenly moved downwardly, to open port 21to port 26, there would be a tremendous hydraulic shock or hammering inthe lines, as has been true in the past. However, with out improvedsystem, to lower the ram the solenoid 49 is merely deenergized bypressing the switch 61, permitting valve 48 to return to the positionwith port B connected to T and port A connected to P. This permits arestricted flow of oil out of the pilot end of the valve 22 and into thereservoir 15, but the high pressure in the main line 17 causes oil toflow through lines 42, 39 and 38 preventing piston 23 from movingdownwardly. The pilot line 46 may be a very small line, such forinstance as a inch conduit as may be the lines 42, 43 and 39. Thus, assoon as valve 48 is connected as indicated by deenergizing solenoid 49,oil flows through line 42, past check valve 41, line 39, line 38, port37, into the pilot end of valve 22, thence through the valve 48 andreturns to reservoir through lines 52 and 27, and line 53. Due to thesmall size of the pilot lines and valve 48, there is no shock tothe'hydraulic system, the oil bleeding off and allowing the ram to movedown at first very slowly. As the hydraulic pressure in the pilot end23b of valve 22 now is essentially the same as the pressure at the otherend 23 of valve 22 and this pressure is at first high, the differentialin area between 23 and 23 (for example, 1 square inch) will cause ahydraulic unbalance larger than the force of spring 28. Thus, theplunger 23 remains in its upward or closed position until the main linepressure in lines 17 and 19 drops down into the neighborhood of thatequalling the force exerted by spring 28. At this point the plunger 23begins to move downwardly as viewed in FIG. 1, thus to open at thesealing seat 24. This opens the large port 2-1 to the large port 26,whereupon the ram piston 11 begins to move downwardly very rapidly. Atthis point in order to roll the bale off the ram platen, the ram platenmust be stopped. This is accomplished simply by momentarily closing thestop switch numbered 62. This has the effect of energizing the solenoid49 and starting the pump motor 13 momentarily. The momentaryenergization of the pump motor provides sufiicient fluid to again movethe plunger 23 of the Valve upwardly to close ofi port 21 from port 26as described in the first step of the operation. After the bale isrolled oft the ram platen the ram is moved upwardly about two feet todress the block, that is to put the bagging on the follow block carriedby the plunger '11. This is done by pressing the up button to energizethe electric motor driving the pump, solenoid 49 remaining energized. Tostop the ram while dressing the block the stop button 62 is pushed. Thisstops the pump from running while solenoid 49 remains energized. It willbe noted that in this condition the check valves 41 and 44 are needed toprevent the plunger of valve 22 from opening. To allow the ram to lowerto its bottom position for turning the press, the down switch 61. ispressed, deenergizing solenoid 49, permitting valve 22 to openimmediately, it being understood that the pres sure in the main line isnow well below the pressure exerted by the spring 28.

It will be apparent from the foregoing that the completely shocklessoperation of our improved system permits push button control with thepump unit mounted in any position relative to the press. Our inventionalso requires only one line from the pump unit to the ram of the press.by the spring 23 with the differential in area of the ends of theplunger 23 of valve 22, our improved system can be made to cause themain valve to open at any desired pressure in the system. It willfurther be understood that very smallquantities of fluid only need bedrained from the main system through the pilot valve 48 before thepressure is lowered sufiiciently to permit safe, shockless opening ofthe main valve 22.

Referring now to FIGS. 4 and 5 of the drawings we show a modification ofour invention adapted for association with a double acting ram. Forpurposes of illustration we show a ram 81 having therein a piston 82 andshown diagrammatically on the piston 82 is a follow block 33. The block8-3 is designed to press against a bale of cotton or other material tocompress it to around 2,000 pounds per square inch. Also, instead ofpacking upwardly as does the rain it? of FIG. 1, the ram 81 packsdownwardly.

The main control valve 84 may be a type of valve having an outer casing86 and a spool 87. The spool is biased to center position by springs 38and 89. Further, the ends of the spool are provided with pilotconnection openings 91 and 92; A port 93 is adapted to be connected by aline 94 to the top of the ram 31. A port 96 is adapted to be connectedby a line hi to the lower end of the ram.81. Pressure is supplied to aport 98 through a line 99 from a pump 1M driven by an electric motor102. Fluid returns to the tank or reservoir 163 through a line 104connected to a port 1% in the valve body.

As seen from FIG. 5, spool 67 is provided with a restricted passage M7.The restricted passage connects the pressure port 98 to the tank port1-06 whenever the valve is in centered position as shown in FIG. 5. Thepurpose of this restricted passage will be later explained.

At 103 we show a pilot valve for controlling the main valve 84. Thevalve 108 may embody a housing and spool shown diagrammatically in FIG.4. The spool is connected by a link 109 to a shaft 111 which is undercontrol of an operating handle 112. The shaft 111 also carries a earn113 which rotates to the right or left as viewed in FIG. 4 whenever thehandle 112 is pushed downwardly or upwardly, respectively. The motor 102is under control of a switch 114 having a switch arm 116. The end of theswitch arm falls into a notch 117 in the periphery of the cam 113whenever the parts are in the center position shyown, opening switch 114and deenergizing pump motor 1 2.

It will be seen that the pressure line 99 is connected by means of aline 11$,througl1 a check valve 119 to the pressure port P of valve 108.The return line 3104 is connected by a line 121 to the return port R ofvalve 108.

A' pilot line 122 connects a port labeled 2 of valve 108 to the pilotconnection port 92 of valve 84. Another pilot line 123 connects the portnumbered 1 of valve 108 to the pilot connection port 91 of valve 84. Aline 124 having therein a check valve 126 connects line 123 to the line94- leading to the top of ram 81.

A line 127 is connected to line 118 between the valve 119 and line 99and leads to a spring pressure relief valve 128. The valve 328discharges through a line 129 to a By properly proportioning the forceexerted" amass? unit 131 which in effect is a hydraulic cylinder. Thepiston 132 of the cylinder 131 carries a plate 133 on its upper end andwhich cooperates with the lower section 134 of the cam 113 in order tocenter the cam whenever a pres sure in excess of the setting of reliefvalve 128 occurs in line 127. Still another pilot line 135 havingtherein a check valve 137 is connected to the line 97 and leads also toa port 138 in the hydraulic cylinder 131 and connects along its lengthto line 121. A pressure gauge 139 may be provided in the circuit ifdesired. Also, a line 141 leading from the lower end of the cylinder 81,past the packing glands, may be used to drain off into a container 142any fluid that passes the packing.

The operation of the double acting system just described is as follows:

Starting with the ram in the upward position the operator moves thecontrol handle 112 downwardly. This closes switch 114, energizing motor102, starting the pump which supplies fluid under pressure to line 99.Simultaneously through link 109, pilot valve 103 is shifted so that itsport P is connected to its port numbered 1 and the port R is connectedto the port numbered 2. Oil from the pump flows to the main valve 84,through the restricted passage 107 and back to the tank 103 through line104. Due to the restriction of the passage 107 there will be built up apressure, which, by way of example, may be around 400 pounds. Thispressure will cause oil to flow down the pilot line 118 to the port P ofvalve 108. This oil will continue out the port numbered 1 of valve 103up to the pilot connection 91 of valve 84. This shifts the spool 86downwardly as viewed in FIG. 5, connecting port 93 with 98 and port 96with 106 of the valve 84. This supplies oil under pressure to the top ofthe ram through line 94, oil in the bottom of the ram returning throughline 97, port 96, port 106 and back to tank through line 104. In view ofthe fact that no more pressure than a maximum of, say, 400 pounds, isallowed to build up due to the restricted passage 107, the shifting ofthe spool 87 in the main valve 84 occurs without any shock.

With the top of the ram connected to the pressure line from the pump andthe bottom of the ram connected to the tank line, the ram will descendand will continue down until either the operator shifts the handle 112back to center, or stop position, or until enough pressure builds up inthe pressure line 94 due to the resistance of the block 83 against thebale to open the relief valve 123. Once the relief valve 128 is openedoil is allowed to flow to the bottom of the plunger or piston 132 of thecylinder mechanism 131, raising the piston 132 and causing the cam blade133 to engage the cam surface 134, thus to center the cam 113 to theposition shown in FIG. 4. Oil in cylinder 131 flows to the bottom of theram through restricted line 136. In other words, by employing the reliefvalve 128, piped as shown, the pressure on the bale and hence itsdensity is automatically determined since a given pressure in the line99 causes the recentering of the control cam 113. In the center positionof the cam valve 108 has its ports 1 and 2 connected, while isolatingthem from either the pressure line from the pump or the return line tothe reservoir. This causes an equal pressure to be exerted on either endof the main operating valve spool, permitting the springs in the valve8-!- to center its spool. Centering of the spool blocks off both the topand bottom of the ram from any oil flow either in or out by blockingboth top and bottom of the ram. The ram thus is held rigidly in placewithout the possibility of leakage upwardly. If only the top of the ramwere blocked, then a small seepage by the piston rings in the ram headwould allow the ram to rise because oil could flow out of the bottom ofthe ram as it seeped by the piston rings.

With the ram now pressing very hard against the bale and at a pressureof, say, 2,000 pounds, this pressure is present in the lines leadingfrom the top of the ram. If the large main operating valve 84 weresuddenly opened under this pressure, there would be tremendous hydraulicshock. However, with our improvement when the handle- 112 is movedupwardly the pump is energized and the pilot valve 108 is shifted toalign its port numbered 1 with its port R and with its port 2 connectedto its port P. Such alignment results ultimately in the spool 87shifting to connect the top of the ram with the tank line and the bottomof the ram with the pressure line from the pump. However, initially thespool 87 is in the center position and in view of the fact that only apressure of, say, 400 or 500 pounds can be developed by the pump due tothe throttling passage 107, the 2,000 or so pounds of pressure in theline from the top of the ram will not allow the spool of the main valve84 to shift. This is due to the provision of the line 124 leading fromconnection 91 to line 94. The check valve 126 in line 124 allows oil toflow only from the top of the ram to the pilot connection 91 or throughline 123. Therefore, the pilot connection 91 of the valve 84 will, atthis time, have 2,000 pounds per square inch force, whereas there isonly 400 or 500 pounds per square inch force available to push againstthis pressure on the other pilot end of the main valve. It is apparentthat this unbalance would actually cause the spool in the main valve tomove in the opposite direction were it not for the check valve 119. Itis the check valve 119 which prevents the spool 87 from shiftingdownward from center as viewed in FIG. 5. Since the port numbered 1 ofvalve 108 is now connected to the port R of that valve, oil is free toflow from the top of the ram through the pilot lines and to the tank. Itis here to be noted that the pilot lines 118, 121, 122, 123,

127, 129 and 136 are very small compared to the main hydraulic lines.Consequently there is no hydraulic shock as this oil bleeds olf. The ramthen slowly moves upward under the force of the bale, expanding againstthe ties which by now have been placed around it, as the pressure bleedsoff through the pilot lines. It will be understood, of course, that thispressure drops 011 very rapidly and actually in about two seconds it hasreached the 400 to 500 pounds per square inch level below which thepressure developed in the pressure line from the pump causes the pilotpressure on the lower end of the main valve 34 to move its spoolupwardly. This movement will then align the port 93 with the port 106,permitting oil in the top of the ram to flow to the tank. At the sametime the port 96 will be aligned with the pressure port 98, providingoil under pressure to the bottom of the rain. The ram will then moveupwardly at a very rapid ra e.

The line 136 and check valve 137 are used to assure against thepossibility of air entering the bottom of the ram through the rampacking during the bleeding off period of the up movement of the rambefore the main valve shifts.

From the foregoing it is apparent that we have provrded an improvedhydraulic system in which we have substantially eliminated all hydraulicshock when depressurrzing a hydraulic cylinder, ram, or other pressuredevice. By causing the pilot valve automatically to delay movement ofthe main valve while the pilot valve bleeds off the high pressure oil,we provide a system which is fully automatic, inexpensive, simple andsubstantially trouble free. In this specification and the appendedclaims, the expression hydraulic cylinder is intended to include alsoother pressurizable devices in which there exists the problem ofdepressurizing the same as set out herein. It is to be especially notedthat in both modificatrons the main valves are caused automatically tofollow the settings of the pilot valves, and that operating pressuresfor the main valves are derived from the ram operatmg pressure sources.

While we have shown our invention in two forms, it will be obvious tothose skilled in the art that it is not so limited, but is susceptibleof various other changes and modifications without departing from thespirit thereof, and we desire, therefore, that only such limitationsshall be placed thereupon as are specifically set forth in' the appendedclaims.

What We claim is:

1. The combination with a hydraulic cylinder and a high pressure line tosupply fluid under pressure to one end of the. cylinder, of ahydraulically actuated main flow control valve in the high pressureline, a pilot valve, a line connecting the pilot valve to the highpressure line in fluid by-passing relation to the main valve and when inone position efiective to discharge fluid directly from the highpressure line, a pair of hydraulic operating lines running directly fromthe pilotvalve to the main valve and effective immediately upon givensettings of the pilot valve to cause corresponding settings of the mainvalve, means to open the pilot valve before opening the main valve whenthe cylinder is pressurized, whereby a quan tity of high pressure fluidacting on the cylinder is discharged from the cylinder through the pilotvalve without opening the main valve, and means operable subsequently tothe opening of the pilot valve to relieve the hydraulic operatingpressure on the main valve, thereby minimizing hydraulic shock uponopening of the main valve.

2. The combination with a fluid pressure cylinder and a source of fluidunder pressure, of a hydraulic pressure actuated main valve having apart movable by fluid under pressure selectively to a position to admitfluid to the cylinder and to a position to shut the cylinder off fromthe source of fluid under pressure, a pilot valve hydraulicallyconnected by a pair of hydraulic lines to the main valve and effectiveimmediately upon movement to selected positions to move the movable partof the main valve to corresponding selected positions, and hydraulicconnections between the pilot valve and the cylinder through which aquantity of fluid under pressure in the pressurized end of the cylindermay be drained 01f without passing through the main valve, whereby thecylinder may be partially depressurized prior to opening of the mainvalve.

3. The combination with hydraulic cylinder and a pressure line to supplyfluid under pressure to one end there of, of a main valve having apressure actuated movable part controlling the flow of fluid into andout of the cylinder, a pilot valve, a line connecting the pilot valve tothe pressure line, another line connecting the pilot valve in operatingrelation to the pressure actuated movable part of the main valve, meansto move the pilot valve eflective hydraulically to shift the movablepart of the main valve to a position to admit fluid under pressure tothe cylinder by creating a hydraulic unbalance at one end of saidmovable part, and means to move the pilot valve to a position initiallyby-passing the main valve to drain off high pressure fluid from thecylinder when pressurized and subsequent thereto to remove the hydraulicunbalance on the main valve and allow passage of fluid therethrough,thereby substantially to eliminate shock upon movement of the main valveto position for fluid to flow therethrough from the cylinder.

4. In a system of the class described, a fluid pressure cylinder, atsource of fluid under pressure, a main valve having a movable partcontrolled by fluid under pressure to admit fluid to the cylinder, toshut off fluid from the cylinder and to discharge fluid from thecylinder, a pilot valve, hydraulic connections from the pilot valve tothe movable part of the main valve and e'nective to shift the main valvemovable part to predetermined fluid admitting, fluid holding and fluiddischarge positions in accordance with predetermined settings of thepilot valve, means other than hydraulic pressure urging the movable parttoward position to discharge fluid from the cylinder, said hydraulicconnections embodying means hydraulically to unbalance the movable partof the main valve and thereby move it to a selected position one ofwhich is a position to admit fluid under pressure to the cylinder and tohold the fluid in the cylinder, and means included in the l0 hydraulicconnection to bleed oil a quantity of fluid from the pressurized end ofthe cylinder while still holding the movable part of the main valve influid holding position, wherebythe pressure in the cylinder is reducedprior to releasing the movable part of the main valve to the action ofsaid means urging the movable member toward fluid discharging position.

5. In a system of the character described including a hydraulic cylinderand a line leading to the cylinder and connected to a source of fluidunder pressure, a main valve in said line controlling the admission anddischarge of fluid to and from the cylinder, said valve embodying afluid pressure actuated movable part for opening and closing the same, apilot valve, hydraulic lines connecting the pilot valve to the mainvalve and disposed upon admission of fluid under pressure thereto tomove the movable part to selected main valve positions, fluidconnections from the fluid pressure line to the valve in bypassingrelation to the main valve, means to shift the pilot valve to a positionto pass a part of the fluid from the cylinder when pressurized throughsaid by-passing fluid connection without changing the position of themovable part of the main valve, thereby partially to depressurize thecylinder, and means operable subsequently to the partialdepressurization of the cylinder to decrease the fluid pressure in thepilot lines connecting the pilot valve to the main valve, whereby themain valve may then be moved to a position to discharge fluid from thecylinder.

6. The combination with a single acting hydraulic ram and a source offluid under pressure, of a line leading from the pressure source to theram, a main valve in said line controlling the admission and dischargeof fluid from the ram, said valve embodying a movable part in the formof a diflerential hydraulically actuated piston which in one positionconnects the ram to the source of fluid under pressure and in anotherposition discharges fluid from the ram, said pressure line beingconnected to exert force on the smaller end of said diflerential piston,means urging the piston toward fluid discharge position with a totalforce less than the total force generated by application of the maximumworking pressure on the cylinder when applied to the larger end of thepiston, a pilot line leading from the source of fluid under pressure tothe larger piston end of the main valve, a pilot valve movable from aposition to block flow of fluid from the large p'iston end of the mainvalve, and means to urge the pilot valve to a position to drain ofl apart of the fluid from the pressurized end of the ram while maintainingthe main valve piston in closed position, whereby the piston shifts toram fluid discharge position only after the ram is depressurized belowthat required to overcome said means urging the piston toward fluiddischarge position.

7. Apparatus as defined in claim 6 in which the pressure line isprovided with a spring loaded check valve eflective to produce higherfluid pressure in one part of the pressure line than in the part thereofconnected to the small piston end of the main valve, and in which thepilot line leading to the large diameter piston end of the valve is alsoconnected to the higher pressure part of the pressure line, and in whichthere are check valves in the pilot line just named to pass to thelarger diameter piston ends fluid under pressure from whichever sectionof the pressure line is under greater pressure, but not in the reversedirection.

8. The combination with a double acting hydraulic ram and a source offluid under pressure, of a main valve controlling the admission anddischarge .of fluid to the ram and embodying a movable part shiftable tofluid supply and fluid discharge position upon the application of pilotline fluid pressure thereto, main lines connecting the main valve to theupper and lower ends of the ram,

said main valve embodying means urging its movable I part towardposition to trap fluid in both ends of the ram, :1 pilot valve, pilotlines connecting the pilot valve 9. Apparatus as defined in claim 8 inwhich the pilot to the main valve whereby upon moving the pilot valvevalve is manually operated;

to selected positions the main valve is moved selectively to fluidadmitting, fluid trapping, and fluid discharge po- References Cited illthe file of this Patent sitions, a bleed line connected to the highpressure end 5 of the ram and to the pilot valve effective when thepilot UNITED STATES PATENTS valve is in one position to bleed oil aquantity of fluid 2,220,929 Stratton Nov. 12, 1940 from the ram whenpressurized while holding the main 2,351,317 Carnerota June 13, 1944valve in fluid trapping position, whereby the ram is par- 2,362,864Towler Nov. 14, 1944 tially depressurized prior to moving the same toram 10 2,590,137 Towler et al Mar. 25, 1952 fluid discharge position.2,609,794 Towler et al. Sept. 9, 1952

1. THE COMBINATION WITH A HYDRAULIC CYLINDER AND A HIGH PRESSURE LINE TOSUPPLY FLUID UNDER PRESSURE TO ONE END OF THE CYLINDER, OF AHYDRAULICALLY ACTUATED MAIN FLOW CONTROL VALVE IN THE HIGH PRESSURELINE, A PILOT VALVE, A LINE CONNECTING THE PILOT VALVE TO THE HIGHPRESSURE LINE IN FLUID BY-PASSING RELATION TO THE MAIN VALVE AND WHEN INONE POSITION EFFECTIVE TO DISCHARGE FLUID DIRECTLY FROM THE HIGHPRESSURE LINE, A PAIR OF HYDRAULIC OPERATING LINES RUNNING DIRECTLY FROMTHE PILOT VALVE TO THE MAIN VALVE AND EFFECTIVE IMMEDIATELY UPON GIVENSETTINGS OF THE PILOT VALVE TO CAUSE CORRESPONDING SETTINGS OF THE MAINVALVE, MEANS TO OPEN THE PILOT VALVE BEFORE OPENING THE MAIN VALVE WHENTHE CYLINDER IS PRESSURIZED, WHEREBY A QUANTITY OF HIGH PRESSURE FLUIDACTING ON THE CYLINDER IS DISCHARGED FROM THE CYLINDER THROUGH THE PILOTVALVE WITHOUT OPENING THE MAIN VALVE, AND MEANS OPERABLE SUBSEQUENTLY TOTHE OPENING OF THE PILOT VALVE TO RELIEVE THE HYDRAULIC OPERATINGPRESSURE ON THE MAIN VALVE, THEREBY MINIMIZING HYDRAULIC SHOCK UPONOPENING OF THE MAIN VALVE.